This invention relates to the art of platemaking, and in particular to a gravure printing plate blank, or half-finished gravure printing plate, which can be readily and repeatedly processed into a completed printing plate. The invention also particularly concerns a process for the fabrication of the gravure printing plate blank. The terms "printing plate" and "printing plate blank", as used herein and in the claims appended hereto, should be interpreted in a broad sense, as they are intended to connote those in the form of a solid cylinder; indeed, in some instances, these terms will be used synonymously with "printing cylinder" and "printing cylinder blank" respectively.
There exist many and varied types of gravure printing plates in current usage. Among these are "conventional gravure" printing plates, intaglio halftone gravure printing plates, those formed by electronic and other engraving processes, and those utilizing plastics. The first recited conventional gravure makes up the mainstream of gravure platemaking.
The preparation of a printing plate or cylinder by the conventional gravure method starts with the copper-plating of an iron or steel cylinder. Silver and copper are then plated successively over the copper-plated cylinder. The silver plating serves as a stripping layer, and the outer copper plating forms the so-called Ballard layer. A subsequent grinding of the Ballard layer provides a smooth-surfaced printing plate blank.
For processing this blank into a printing plate, ready for printing operation, a sensitized carbon tissue is exposed through a gravure screen and a continuous-tone positive. The exposed carbon tissue is then placed over the above prepared blank and is developed to provide an etching resist. An etching operation is then performed on the blank through the resist, thereby forming ink-retaining cells or depressions of equal surface area but of unequal depth. After removal of the resist the printing plate is usually chromium-plated for longer printing life.
Upon completion of required runs of printing operation the Ballard layer is stripped from the cylinder together with the silver stripping layer. The cylinder subsequently undergoes the steps of silver and copper plating and so returns to the blank state. The process set forth in the preceding paragraph is then repeated for delineation of a new printing image on the blank. Thus the operations of gravure platemaking and remaking according to the prior art involve unnecessary complex, time-consuming and costly processes, necessitating wasteful use of copper.